1. Field of the Invention
The present invention relates to the field of an image forming apparatus comprising a liquid ejection head, and more particularly, to a liquid ejection head, a method of manufacturing the same and an image forming apparatus comprising the same in which ejection ports which eject liquid are arranged at a high density, and liquid flow channels are simplified.
2. Description of the Related Art
Conventionally, as an image forming apparatus, an inkjet printer (inkjet recording apparatus) is known, which comprises an inkjet head (liquid ejection head) having an arrangement of a plurality of nozzles (ejection ports) and which records images on a recording medium by ejecting ink from the nozzles toward the recording medium while causing the inkjet head and the recording medium to move relatively to each other.
In an inkjet printer of this kind, ink is supplied to pressure chambers from an ink tank, via an ink supply channel, and by driving piezoelectric elements by supplying electrical signals corresponding to the image data to the piezoelectric elements, the diaphragms constituting a portion of each pressure chamber are caused to deform, thereby reducing the volume of the pressure chamber and causing the ink inside the pressure chamber to be ejected from a nozzle in the form of a droplet.
In an inkjet recording printer, one image is formed on a recording medium by combining dots formed by ink ejected from the nozzles. In recent years, it has become desirable to form images of high quality on a par with photographic prints, in inkjet printers. It has been thought that high image quality can be achieved by reducing the size of the ink droplets ejected from the nozzles by reducing the diameter of the nozzles, while also increasing the number of pixels per image by arranging the nozzles at high density.
In order to achieve high density of the nozzles, it is indispensable to devise the composition of the electrical wiring and the ink flow channels suitably. Therefore, conventionally, there have been various proposals for achieving high density of the nozzle arrangement, as well as improving the ink supply efficiency and increasing the printing speed.
For example, it is known that high density of the nozzles can be achieved by providing ink supply channels for supplying ink to the pressure chambers in a diaphragm forming one surface of the pressure chambers, and also forming a reservoir (common liquid chamber) on the rear surface of the diaphragm in such a manner that ink is supplied to the pressure chambers from the reservoir by means of the ink supply channels (see, for example, Japanese Patent Application Publication No. 9-226114).
Furthermore, for example, it is also known that the structure can be simplified by providing piezoelectric elements on the surfaces of the pressure chambers opposite to the surfaces on which nozzles are provided, providing a portion of a reservoir for supplying ink on the side adjacent to the piezoelectric elements, and providing a covering on the piezoelectric elements, in such a manner that electrodes can be extracted by wire bonding, thin film formation, or the like (see, for example, Japanese Patent Application Publication No. 2000-127379).
Furthermore, for example, it is also known that higher density and lower costs can be achieved by disposing piezoelectric actuators on pressure chambers, on the nozzle surfaces thereof, adopting a structure in which aluminum plugs pass through laminated layers, and then performing silicon photoetching to form an inkjet head (see, for example, Japanese Patent Application Publication No. 2000-289201).
Moreover, for example, it is also known that an increased number of nozzles, reduced costs and high accuracy can be achieved, by providing supply restrictors in a diaphragm, providing an ink supply tank forming an ink supply section on the opposite side of piezoelectric elements from the pressure chambers, forming ink supply ports connecting to the pressure chambers from the ink supply tank and passing through the diaphragm, and furthermore, causing the ink supply section to act as an insulating sealing cover for the piezoelectric elements, and thus providing covering and damping functions for the piezoelectric elements (see, for example, Japanese Patent Application Publication No. 2001-179973).
Furthermore, for example, it is also known that by using a porous material having a large number of small internally connected pores, such as a sintered stainless steel member, in the ink supply layer, then passage of ink through same becomes possible, refilling properties are improved, high printing speed and high reliability are achieved, and an inkjet head having excellent ink preparation characteristics and filtering characteristics for a plurality of types of ink is obtained (see, for example, Japanese Patent Application Publication No. 2003-512211).
However, for example, in the devices described in Japanese Patent Application Publication Nos. 9-226114, 2000-127379 and 2001-179973, if a common flow channel (common liquid chamber) or a portion thereof is formed on the opposite side of a piezoelectric body from the diaphragm and the pressure chamber, then in order to achieve higher density and a higher ejection driving speed (higher driving frequency), since only the pressure chamber and the nozzle are disposed on the pressure chamber side due to the available space on the pressure chamber side, a supply channel (supply port) must be formed in the diaphragm and the common flow channel must pass completely through the diaphragm to the other surface (on the side opposite to the pressure chamber). Furthermore, the electrical wires, and the like, for supplying drive signals to the piezoelectric bodies, must be wired at high density. However, in this case, if the electrical wires are extracted on the same surface as the piezoelectric bodies, then a multi-layer flexible cable is required, which presents a large problem in terms of installation technology.
Furthermore, in the device described in Japanese Patent Application Publication No. 9-226114, actuators (piezo elements) are arranged at 1440 dpi in one row, but there is no description relating to the wiring, and hence the disclosure is not especially practical and even higher density is difficult to achieve.
Furthermore, in the device described in Japanese Patent Application Publication No. 2000-127379, a portion of the common liquid chamber (reservoir) is provided on the side adjacent to the piezoelectric elements, but since a portion of the common liquid chamber is naturally situated on the side adjacent to the pressure chambers, and since the common liquid chamber is also provided further toward the outer side of the piezoelectric elements than the electrical wiring surface, then it is not suitable for high density.
Furthermore, in the device described in Japanese Patent Application Publication No. 2000-289201, there is a piezoelectric actuator on the nozzle side, and a common liquid chamber is provided on the piezoelectric actuator side (and hence the nozzle side) in such a manner that a unified IC is formed, in addition to which, electrical wires (aluminum plugs) are formed perpendicularly from the drive circuits. However, since the common liquid chamber is formed on the outer side of the piezoelectric actuators, and the aluminum plugs are formed so as to pass through the laminated layers in positions separate from the piezoelectric actuators and the common liquid chamber, then space for forming the plugs is required, and hence high density is difficult to achieve.
Moreover, in the device described in Japanese Patent Application Publication No. 2001-179973, pores for supplying ink are provided in the regions of a diaphragm made of zirconia where no piezoelectric elements are situated, but since the wiring is situated on the piezoelectric element surface, then whatever the shape of the elements, it is particularly difficult to apply to a matrix structure and high density is difficult to achieve.
Furthermore, in the device described in Japanese Patent Application Publication No. 2003-512211, bumps are formed on both surfaces of an insulating plate, in such a manner that the piezoelectric elements are pressurized by elastic pads and electrodes are extracted, but high density is difficult to achieve, and the connections are also liable to become instable.